DNA bending and expression of the divergent nagE-B operons.
Repression of the divergent nagE - B operons requires NagC binding to two operators which overlap the nagE and nagB promoters, resulting in formation of a DNA loop. Binding of the cAMP/CAP activator to its site, adjacent to the nagE operator, stabilizes the DNA loop in vitro. The DNA of the nagE-B intergenic region is intrinsically bent, with the bend centred on the CAP site. We show that displacement of the CAP site by 6 bp results in complete derepression of the two operons. This derepression is observed even in the absence of cAMP/CAP binding and despite the fact that the two NagC operators are still in phase, demonstrating that the inherently bent structure of the DNA loop is important for repression. Since no interaction between NagC and CAP has been detected, we propose that the role of CAP in the repression loop is architectural, stabilizing the intrinsic bend. The cAMP/CAP complex is necessary for activation of the nagE-B promoters. In this case protein-protein contacts between CAP and RNA polymerase are necessary for full activation, but at least a part of the activation is likely due to an effect of CAP binding altering DNA structure.
Plumbridge
J
J
Institut de Biologie Physico-chimique (UPR9073), 13 rue P. et M. Curie, 75005 Paris, France. plumbridge@ibpc.fr
Kolb
A
A
D000117:Acetylglucosamine / Q000378:metabolism; D019747:Aldose-Ketose Isomerases / Q000235:genetics; D019677:Artificial Gene Fusion; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D001693:Biological Transport, Active; D002373:Cyclic AMP Receptor Protein / Q000235:genetics / Q000378:metabolism; D004269:DNA, Bacterial / Q000737:chemistry* / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D007763:Lac Operon; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D009876:Operon
D002373:Cyclic AMP Receptor Protein; D004269:DNA, Bacterial; C020582:glucosamine-6-phosphate isomerase; D019747:Aldose-Ketose Isomerases; D000117:Acetylglucosamine